This invention is concerned with film technology and more particularly with window films. In accordance with this invention, the optical properties of a window film when applied to a substrate are enhanced by use of an application process and solution wherein haze between the window film and the window is eliminated. As a result of this enhancement a film may be retrofitted to a substrate in such a manner that a degree of clarity is obtained which is not possible using prior art application process.
The application or retrofitting of films to windows and other substrates for various purposes is quite common. In the most common applications, films are applied to windows, for example, polymeric or glass panes. Films can also be applied to window panes to affect the ability of these panes to absorb or transmit heat or ultraviolet (UV) light. Further, films can be applied in order to change the color of a window pane. Likewise, films can be applied in order to increase the strength of a window pane and in particular, the ability of the window pane to stay intact after an impact by a foreign object. Films are also applied to window panes in order to alter the ability of the window pane to transmit, absorb or reflect visible and invisible solar radiation. In all applications of films, it is desirable that there be no haze between the film and the substrate. This invention is concerned with a process whereby a window film may be applied in such a manner that there is no haze at the interface between the window and window film. Further this invention is concerned with the interaction of a mounting solution with the pressure sensitive adhesive which is an integral part of the film. More particularly, this invention is concerned with window film mounting solutions which will not react with the pressure sensitive adhesive in such a manner as to create a haze. In the prior art, haze is quite common. This haze results from the fact that certain components of the mounting solution are not compatible with the pressure sensitive adhesive which is used in the application of the film to a substrate.
In the preferred embodiment, a window film is retrofitted to a substrate via the following procedure.
1. Clean the substrate surface with water, soap, or organic solvent;
2. Spray a mounting solution on to the substrate surface and pressure sensitive adhesive surface of the window film;
3. Remove excess mounting solution;
4. Apply the window film to the substrate such that the pressure sensitive adhesive surface faces the substrate,
5. Properly position the window film on the substrate surface,
6. Squeeze out all excess mounting solution;
7. Allow the film to dry;
It is points 2 and 7 as set forth above that this invention is concerned with. Prior art mounting solutions comprise water which incorporates a wetting agent. While the applicant is not sure, he is of the opinion that a haze development during step 7 above is the result of the wetting agent in the mounting solution being incompatible with the pressure sensitive adhesive in such a manner that a two phased interface results. To an observer this two phase system appears as a haze because of light scattering. With this invention, it is possible to eliminate the alteration of the pressure sensitive adhesive in such a manner that the pressure sensitive adhesive remains as a single phase and hence films as applied in accordance with this invention are haze free. A haze results in the prior art as a result of local fluctuations in the refractive index at the interface of the various phases present. In its broadest terms, this invention relates to the utilization of mounting solutions which will not react with the pressure sensitive adhesive which is used to mount films to a substrate.